The present invention concerns an electronic circuit board for use in the high temperature testing of electronic devices and a method for conducting such tests. Such boards are commonly referred to as burn-in boards. The circuit board of the present invention comprises a base made of steel which is coated with a dielectric layer.
The high temperature testing of electronic circuit devices is commonly employed in the semiconductor or microelectronic device manufacturing industries. Such tests are utilized in the burn-in, TDDB (time dependent dielectric breakdown) and the electromigration testing of semiconductor devices or chips.
Burn-in testing comprises the application of thermal and electrical stresses for the purposes of inducing the failure of marginal microelectronic devices having inherent defects resulting from manufacturing aberrations which cause time and stress dependent failures. TDDB testing concerns monitoring a device for diminished electric properties during heating. Electromigration in thin metal lines can cause chip failures with the formation of voids, or gaps, in interconnects. The potential for electromigration failures is a more significant issue in standard aluminum metal interconnects as chip makers attempt to reduce resistance using thinner wires. Copper metal interconnects are more resistant to electromigration. However, migration is still a concern and this concern has resulted in the need for testing procedures at elevated temperatures. These various elevated temperature tests are run both for the end-run qualification of chips and also for chip developmental purposes. These tests can also be run as a quality control test for incoming electronic devices or chips.
During all elevated temperature testing procedures, the electronic devices are loaded into sockets which make temporary electrical contact with the device leads. The sockets are mounted on high temperature circuit boards with circuitry to provide the proper voltages and electric stimuli to the devices. These circuit boards, which are used in electromigration, TDDB and burn-in testing, are commonly referred to as xe2x80x9cburn-in boards.xe2x80x9d Once the boards are filled with devices, the boards are then loaded into a heating device, such as a convection oven, which in addition to supplying heat also provides an electrical interconnect between the boards and the power supplies and signal generators used to power the electronic devices during heating. During heating, the electrical characteristics of the electronic devices are continually monitored, logged and made available for analysis. The oven, power supplies and signal generators are commonly referred to as the burn-in system.
In the prior art, many burn-in boards were constructed of phenolic/epoxy materials. However, such boards present a major drawback. Specifically, such boards degrade quickly at elevated temperatures (e.g., temperatures in excess of about 180xc2x0 C.). Ceramic substrates are employed for tests run at elevated temperatures (e.g., 300xc2x0 C.), however, ceramic substrates are costly and they must be limited in size, for they are somewhat fragile. Boards comprising porcelain enamel coated steel substrates have also been used in the prior art to produce burn-in boards. These boards have been sold by the ECA Electronics Company of Erie, Pa., under the trademark ELPOR. However, such boards display a leakage current of about 40xcexc Amps or more at 350xc2x0 C. For the testing of current generation electronic devices, there is a need for boards that display a leakage current of less than about 10xcexc Amps. Accordingly, there is a need for a robust high-temperature burn-in board which displays excellent electrical properties that can be produced at a reasonable cost.
The present invention provides a new and improved electronic circuit board or burn-in board for use in testing semiconductor chips or other electronic devices at elevated temperature and a method for conducting such tests. The burn-in board is extremely robust and it can be produced at a reasonable cost. Such boards display a leakage current of less than 10xcexc Amps at 350xc2x0 C. Of course, leakage current is a function of board geometry, circuit area and operating temperature. However, burn-in boards generally display a surface area of 70 or more square inches per side, with about 10%-20% of each side printed with circuitry.
In one preferred embodiment the burn-in board comprises a stainless steel base having a dielectric coating formed thereon. The dielectric coating comprises multiple discrete layers of dielectric material. Formed on the dielectric coating is an electrical circuit. The circuit includes a connector region for facilitating attachment to an external electrical source and a mounting region for mounting sockets for supporting and supplying current to the electronic devices during heating. The board displays a leakage current of less than 10xcexc Amps at 350xc2x0 C.
Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.